The present invention relates to a vibrator-type actuator. More particularly to a vibrator-type actuator having a simple construction and using a piezoelectric-vibrator as an electromechanical conversion means.
Vibrator-type actuators using piezoelectric vibrators as the electromechanical conversion means have been intentionally developed for applications in small-sized and high-torque producing devices i.e., precision mechanical equipment such as automatic focusing cameras, printers, copy machines and video cassette recorders, card transferring devices in card identifying apparatuses for use in banks, and as object transferring industrial robot FMSs (Flexible Manufacturing Systems). Ultrasonic motors have been in practical use as such a vibrator-type actuator.
The ultrasonic motors are, generally, classified into three kinds of systems. The first is a so-called "travelling wave-type" or "mode rotation-type"; the second is a "standing wave-type" based upon the standing wave; and the third is a multiresonance-type". The typical structure and operational principle are disclosed in the following papers:
"Ultrasonic Motors Using Piezoelectric Multi-Mode Vibrators" by TAKEHIRO TANAKA et al., JAPANESE JOURNAL OF APPLIED PHYSICS, VOL.27 (1988) SUPPLEMENT 27-1, pp.192-194, "A Piezoelectric Ultrasonic Motor" by AKIO KUMADA, JAPANESE JOURNAL OF APPLIED PHYSICS, VOL.24 (1985), SUPPLEMENT 24-2, PP.739-741, and "Construction of Ultrasonic Motors and their Application" by YOSHIRO TOMIKAWA et al., JAPANESE JOURNAL OF APPLIED PHYSICS, VOL.27 (1988) SUPPLEMENT 27-1, pp.195-197.
However, the conventionally known ultrasonic motors are complex in both the mechanical and circuit structure of the driving circuit for the piezoelectric vibrator, making it difficult to achieve miniaturization and cost reduction.
A paper feed apparatus smoothly feeding a paper to a predetermined position has been employed in the copy machine, facsimile, printer and the like. In the conventional paper feed machine the paper is held by two rollers and is fed by rotating at least one roller through the use of an electromagnetic motor. However, the electromagnetic motor is complex in structure and requires a speed reduction mechanism since it produces an extremely small torque at a low rotation speed. Thus the conventional paper feed apparatus has the disadvantages of being complex, and of being a large-sized structure with attendant high cost.
Furthermore, in the FSM an object to be manufactured (called "work" hereinafter) is linearly moved or transferred by the gears which convert the mechanical rotational movement of the electromagnetic motor into linear movement. Such a conventional work moving apparatus necessitates an electromagnetic motor and gears and is therefore complex in structure and large in size. The movement of the object along a curved rail has also been widely employed in various automatic machines such as an industrial robot as well as an FMS. The electromagnetic motor and gears are also necessary for the industrial robot, causing the same disadvantages as those of the FMS.
As an actuator which converts electrical energy into mechanical energy, an ultrasonic motor is employed. The ultrasonic motor has superior characteristics to the electromagnetic motor. Namely, the ultrasonic motor produces a larger torque at lower rotational speed than an electromagnetic motor of the same size. The conventional ultrasonic motor requires, however, a complex mechanical structure and driving circuit for the piezoelectric vibrator as stated above. As a result, the use of conventional ultrasonic motors makes miniaturization and cost reduction difficult.